The present invention relates to a thermomagnetic recording method employing, for example, irradiation of a laser light beam on a perpendicular anisotropy magnetic film.
In the thermomagnetic recording method which records data on a recording medium where data bits (magnetic domains) are read out by magneto-optical interaction, the recording medium having a perpendicularly magnetizable thin film is initialized by previously orienting the magnetization in one direction perpendicular to the film plane, and bits having perpendicular magnetization reverse to such direction are formed by local heating with irradiation of a laser light beam or the like, whereby binary-coded data are recorded.
In the thermomagnetic recording method, a time is required for erasure of the recorded data (corresponding to the above-described initialization) executed before rewriting the data, so that it is impossible to realize a fast recording operation at a high transfer rate or in other words a realtime overwriting. With regard to this point, there are proposed a variety of recording methods with an overwrite function which eliminates the necessity of such independent erasure time. Out of the known overwrite type thermomagnetic recording methods, the most promising one is a system adopting modulation of an external magnetic field to a recording medium, and another is a two-head system using an erasing head in addition to a recording head. According to the former system with external magnetic field modulation, as disclosed in Japanese Patent Laid-Open No. 60-48806 for example, a recording operation is performed by applying a magnetic field, which is so poled as to correspond to the state of an input digital signal current, to a heating-beam irradiation area on a recording medium with an amorphous ferrimagnetic thin film having an axis of easy magnetization perpendicular to its film plane.
In performing a fast recording operation at a high data transfer rate with such external magnetic field modulation mentioned, it requires an electromagnet operable at a frequency on the order of MHz, and there exist considerable difficulties in production of such electromagnet. Even if the production is technically possible, there still remain some problems with respect to great power consumption and excessive generation of heat to eventually bring about an impediment to practical use. Meanwhile in the two-head system, an additional head is required and the two heads need to be spaced apart from each other, hence imposing a great burden on the drive mechanism with an economical disadvantage and nonadaptability to mass production.